(1) Field of the Invention
The invention relates to a method and a device for deriving and evaluating cardiovascular information from electrocardiograms, especially for telemedical applications.
(2) Description of Related Art
As a consequence of the progression of cardiovascular diseases and the limited therapeutic possibilities in the late stages, there is the necessity of an early and complex cardiovascular diagnosis, during which above all also the interaction of the heart with the rest of the peripheral circulation system has to be assessed at the same point of time and at any time of the day. Most of the hitherto known measuring methods show disadvantages as far as their evaluation is concerned, for both the patient and the responsible doctor who has to derive therefrom a diagnosis. Telemetrical requirements hardly get any attention.
Under the cardiovascular aspect, the electrocardiogram (ECG) based on the known limb and thorax leads represents the most widely spread diagnostics and monitoring method, though it brings along a number of inadequacies because the ECG detects electrical phenomena at the heart, while the entire cardiovascular system is not sufficiently represented. Therefore, there is the necessity to determine additional information contained in the ECG as comprehensively as possible. In consideration of a telemedical application, a device to be developed must take into account the following priorities:                easy and reliable handling,        not dangerous to the user        cost-efficient        easy and modular evaluation possibility for both the doctor and the user.        
In general, telemedicine is a broadly defined comprehensive term which stands for the use of multimedia communication and information technologies in the health sector. In a narrower sense, it describes the actual application of different technologies to render individual services in the field of medical engineering, by simultaneously bridging the physical distance between the doctor and the patient.
Hence, it appears that telemedicine allows a reduction of the relative risk which is, in many cases, caused by claiming medical aid too late and, thus, of the deterioration of the prognosis. A substantial prerequisite for this are the practicability and reliability of the cardiovascular parameters, which the user himself derives and transmits telemetrically.
FIG. 1 shows the general functional diagram of a tele-ECG: recording, transmitting, receiving, analyzing. Significant is here the result of performed analyses: Patients, who were connected to the telemedical service, reacted fast and determined. Nearly 90% of them contact the telemedical center within one hour after the troubles began.
The use of telemedical technologies involves special requirements, which hardly arise with the known ECG recordings.
In the field of the mobile detection and storage of electrocardiogram signals specifically for the use in medicine and sports, the prior art is extensive. Examples are:    DE 197 49 768 A1 (Plaster with data recording function for the detection and storage of electrocardiogram signals), PCT/DE98/033225 (Evaluation of electrocardiograms in the field of extrasystoles), PCT/US99/09336 (Elektrocardiography Electrodes Holder), DE 198 30 316 A1 (Method and device for detecting ventricular fibrillation), WO 99/04687 (Remote Monitoring Apparatus for Medical Conditions), DE 199 02 253 A1 (Method and system for characterizing the quality of cardiac function indicating signals), PCT/US99/03666 (A System and Method for Detecting and Locating Heart Disease), PCT/US98/16693 (Automatic Cardiometer), EP 0 760 225 A1 (Method and apparatus for correcting for non-physiological variations in ECG signals), EP 0 800 787 A1 (Device for monitoring measurements electrodes, devised for picking up physiological measurement signals, and their leads), EP 0 855 167 A1 (Multiple ECG electrode strip), EP 0 864 294 A2 (Detecting abnormal activation of the heart), PCT/GB98/00742 (Method of Analyzing a cardiac signal), DE 195 23 199 A1 (Method for representing ECG signals), DE 195 10 382 A1 (Portable device for detecting ECG data), PCT/US96/02826 (Method and apparatus for detecting artifacts using common mode signals in differential signal detectors), PCT/BE95/00123 (A device and a method for recording and monitoring cardiac activity signals), EP 0 657 136 A1 (Electrocardiograph), DE 199 54 856 A1 (Method and device for detecting a connection error of a telemetrical biomedical device), DE 200 08 602 U1 (Volks-ECG), PCT/AU00/00656 (Cycling event and auto-trigger memory handling), PCT/US99/18296 (Ambulatory physio-kinetic monitor), DE/EP 0 746 229 T1 (Measurement and evaluation of the electrical stability of the heart), PCT/IL00/00506 (Compact electrode assembly for a portable ECG signaling device), EP 1 110 502 A2 (Clinical research workstation), DE 100 65 578 A1 (Method for identifying an electrode placement), DE 102 47 435 A1 (Interpretation manual electrocardiograph), EP 1 157 659 A1 (Method and apparatus for reducing noise and detecting electrode faults in medical equipment), DE 102 45 143 A1 (Method for evaluating electrocardiograms), DE 102 33 071 A1 (Method and system for the measurement, the analysis and the wireless transmission of cardiac potentials), WO 02/24068 A1 (Method and system for detection of cardiac arrhythmia), A 61 B 5/0404 (Portable ECG recorder, Utility Model Document), DE 201 18 850 U1 (Portable measuring device for ECG analysis), DE 203 09 617 U1 (Simulation device to output test signals to electrocardiographs, Utility Model Document), DE 203 06 009 U1 (System for the measurement, the analysis and the wireless transmission of cardiac potentials, Utility Model Document), DE 299 24 092 U1 (ECG recorder, Utility Model Document), EP 0 739 181 B1 (Sudden cardiac death prediction), EP 0 906 058 B1 (Device for the frequency analysis of atrial fibrillation), DE 696 17 564 T2 (Pocket device for the detection of an electric biological signal, especially an electrocardiographic signal).
As is generally known, an electrocardiogram (ECG) represents, in its most general form, the variation of bioelectrical signals or potential differences, respectively, over time, which occur during the depolarization and repolarization in the heart. From this, among others direct indications to arrhythmias or indirect indications to acute myocardial infarctions or post-infarctions can be derived.
Beside the dependency of the (mean) heart rate on the age, it is known from physiology that the activity of the autonomic nervous system significantly influences the heartbeat duration and the entire cardiovascular condition. While a sympathetic stimulation reduces the heartbeat duration by a release of adrenalin and noradrenalin, that is, it increases the rate, it is known that the parasympathetic nervous system causes a heart rate reduction largely by the release of acetylcholine. The latter relates above all to the state when the body is at rest in a horizontal position (vagal stimulation).